[1] maven-dependency-plugin provides number of goals that can be used for extensive dependency analysis
[2] maven-eclipse-plugin allow to generate eclipse project metadata, so project can be imported using import existing project wizard

Maven developer

Debug Maven using Standalone Maven install

First of all you need to get corresponding Maven projects into the Eclipse workspace.

To debug Maven standalone Maven CLI you can set the following environment variable:

Run and Debug Maven 2.1 from Eclipse Workspace with m2eclipse

Debug Maven plugins using m2eclipse

With m2eclipse you can debug Maven core and Maven plugins while running goals using m2eclipse's "Maven Build" external tools launch configuration (or from Run As / Maven * shortcut from the popup menus). Simply put a break point in the corresponding classes and switch to the Debugger perspective.

You can also configure Maven surefire plugin to not fork new JVM to run tests and then you can even debug test classes launched using "Run As / Maven test" shortcut:

Debug Maven using Q4E

Q4E launches Maven in process, not in a new jvm for c. For debugging you'll need a second jvm running in debug mode.

The easiest way to debug both Q4E, Maven and everything run by both of them is to launch a new Eclipse workspace in Debug mode.
Go to Run - Debug and create a new Eclipse Application
In the plugins tab make sure you select all Q4E plugins and click add required plugins
A new Eclipse is launched in debug mode and you could run any Maven goal through the Run - Run Menu, new Maven 2 configuration. Breakpoints in the original Eclipse will be used. Surefire should be configured not to fork the tests in this case.

If you just want to debug tests run by Maven you could configure Surefire plugin to fork with this jvm parameters

When launching a goal that runs the tests the execution will stop just before and you can go to Run - Debug - New Remote Application attaching the remote debugger to port 8000.